December 16, 2010

Pandan and Coconut Tapioca Cake (Banh Bo Nuong) Recipe Challenge

This is one of the strangest things I’ve ever baked. I went three rounds with it as part of a small project with Thu N., who emailed me a while back asking for help in making one of her favorite Vietnamese sweets. If you’re not familiar with banh bo nuong, it’s a chewy, coconutty green cake often sold as slices on Styrofoam trays at Vietnamese bakeries. The color and tropical, grassy notes come from pandan leaves (la dua).

Banh bo hap refers to the Chinese steamed rice cake (bái táng gāo, 白糖糕) that’s sometimes available at dim sum house. Banh bo nuong is the Vietnamese baked version that doesn’t require days of fermentation. It’s supposedly fast to make but it’s taken me a while to figure things out.

The cake is tricky because there is no gluten in it and you have to get it to rise. Additionally, a good banh bo nuong has striations in the cake from the heat pushing through the batter. Those vertical channels – which you see above – are sometimes described as honeycombs, which is why banh bo nuong can be translated as “honeycomb cake.” I see geologic patterns more than patterns formed by busy bees. Ants dig channels like those, right?

So, I’m here to report to you my progress on three (3!) tries. I think you may get a laugh or two, maybe more. Thu’s problem was this: her banh bo nuong was not rising properly in the middle to form the desired ‘honeycomb’ pattern.

The Devil in too many details

There are just a handful of ingredients in this cake -- tapioca starch, sugar, coconut milk or cream, pandan extract, eggs, and leavening. To help Thu, I looked online for a recipe and found several banh bo nuong recipes that specified using single-acting baking powder sold at Vietnamese markets. That’s the pinkish Alsa envelopes below. My mom dug up a recipe from her friend’s daughter that called for Alsa and vanilla sugar, also sold at Vietnamese markets. Some recipes specify a particular brand of tapioca starch too. Below is what I typically use, the 3-headed elephant. Additionally, there was the holiday green pandan extract and a warning to avoid using coconut milk and instead use the thick cream.

Beyond the “you must use this” there were many “you must do that” or your cake won’t rise and bake properly. For example, don’t stir the batter too much. Strain the batter. Let the batter sit for 20 minutes. Preheat the cake pan in the oven. Regulate the oven temperate from high to low. Use a moderate oven temperature. Many people have made this cake at home, and needed to assist Thu, who was pinging me with her progress.

Banh Bo Nuong #1

I gave the recipe from my mom’s friend a try. I made a special trip to Lion market for Alsa single acting baking powder and the Dr. Oetker vanilla sugar. I followed the recipe instructions to what I thought was a “T” but the first cake was frankly, an unmitigated disaster. It took the longest time to rise and I baked the darn thing for 1 1/2 hours!

The green pandan extract turned brown from all that baking. I sent Thu the above photo and she kindly said that it looked nice. I took a bite from that slice and it was rubbery and tasted metallic, most likely from the Alsa baking powder. Worse than all of that – the thing was heavy enough to use as a doorstop or even the rock for a curling competition! I threw banh bo nuong #1 out.

Banh Bo Nuong #2

I reached out to my friend, Terrence Khuu, a San Francisco-based chef. He got his mom’s recipe for me and cryptically sent it via Facebook. Terrence said that she’d been making really good ones that he’d been eating up and getting fat from. Sounded good to me. Mrs. Khuu surprisingly used a 1:1 ratio of tapioca starch and har gow dumpling mix (bot ha cao) that she bought at the Vietnamese market. Terrence sent me a photo of the mix.

Mrs. Khuu did not use Alsa baking powder and food coloring. She simply stirred the ingredients together and baked for 40-45 minutes. I trusted Mrs. Khuu but didn’t buy the dumpling mix. After all the recipe developing for the Asian Dumplings cookbook, I knew that the mix was mostly wheat starch. So I used a 1:1:1 ratio of wheat starch to tapioca starch to coconut cream. I preheated the pan in the oven for about 15 minutes and the cake didn’t rise much at the edge. It seized up instead and deflated a tad after baking.

The cake baked okay but it cracked and weighed just a little less than a doorstop. The pandan extract’s chemically flavor shot right through the tapioca and wheat starches. No wonder Mrs. Khuu didn’t use the pandan extract. Cake #2 went into the trash with a thud.

Banh Bo Nuong #3

I dumped the pandan extract and decided to extract from scratch. I’d done it before with water but this time, used the thin liquid from the canned coconut milk. I chose Aroy-D brand in a box because it’s exactly 1 cup – what I needed for the recipe. Boxed coconut milk and cream are fresher tasting than canned. So I whirred it up and squeezed things dry. Then I stirred all the ingredients together and poured the avocado green batter into a parchment paper-lined baking pan. Into the oven it went for about 45 minutes.

The resulting cake looked like the Elephant Man with that bump you see. Was my oven heat THAT uneven? I let the cake cool and when I went to unmold it, it WOULD NOT come out. I thought I’d lost it. Then I cut and pried out a wedge of the cake. It was gloriously green, not lead-like in weight, and had the vertical honeycomb trenches. I was all smiles! But, the parchment paper was nowhere.

Suddenly, I realized that most of the batter had baked underneath the parchment. The parchment was actually under the crumbly top of the cake! I don’t know if that was because I moved the pan to take the photo or if the direction of heat flow in the batter during baking caused the paper to rise like that. The bump in the cake was caused by an undulation in the parchment paper that is visible below:

In any event, it was the most bizarre baking experience I’d ever had. The cake tasted good and wasn’t as rubbery as an all-tapioca cake. But not having the top of the cake attached was weird. Sometimes, the simplest foods can be the hardest to master.

I think that the recipe is pretty much there but I don’t have the time right now to give it another go. Plus, I depleted my inventory of frozen pandan leaves. But on the next try, I won’t line the pan and hope for the best. Until then, here’s the recipe for you to give it a whirl.

Recipe

Pandan and Coconut Tapioca Cake Banh Bo Nuong

If you don’t have this brand of coconut milk (I got mine at Ranch 99 in a six-pack), use regular canned coconut milk. You want about 1/2 cup of the thin coconut milk and 1/2 cup of the thicker cream. Extracting the pandan in the thin milk is easier to work with. The tapioca and wheat starch are both Asian market items. As for the baking powder, it’s just the regular double acting kind you’d find at a supermarket.

1. Position a rack in the middle of the oven and preheat it to 400F. Oil a high-sided 8-inch round cake pan.

2. Separate the thin from the thick coconut milk. Set aside the thick milk. Use a mini food processor to grind the thinner milk with the pandan.

Then extract the green liquid through a piece of muslin, squeezing as much out as you can. (See this post on pandan for guidance.) Whisk in the reserved coconut cream. Then combine with the eggs, whisking until well incorporated.

3. In a bowl, combine the tapioca starch, wheat starch, salt, sugar, and baking powder. Make a well in the center, then whisk in the liquid ingredients. If the batter is lumpy, pour it through a coarse mesh strainer.

4. Pour the batter into the prepared cake pan and slide it into the oven. Bake for about 45 minutes, until a toothpick inserted comes out fairly dry. There may be a little dampness at the bottom of the cake. Cool on a rack before running a knife around the edge and unmolding.

Good luck and let me know how you do with this recipe! Or, maybe you have experience baking banh bo nuong and want to share your insights? Perhaps you know why the cake bakes up with the vertical striations?